1. The Field of the Invention
The present invention relates to syringes. Specifically, the present invention relates to manually operated hydraulic syringes and methods of manufacture.
2. Prior State of the Art
Syringes are widely used to inject, dispense and extract fluids in a controlled fashion. Conventional syringes generally consist of a syringe body having a cylindrical chamber in which a piston is forced to slide. The chamber has an orifice in the end opposite the piston such that if the piston is pushed towards the orifice, fluid is ejected from the chamber into or onto a target. If the piston is forced away from the orifice, fluid at the orifice is vacuumed into the chamber.
As apparent, a source of force is needed to operate a syringe. A non-human driving mechanism, such as an electrical motor, provides this force in automated syringes. Many syringes, however, operate under the manual force of a user. Although typically less sophisticated than automated syringes, manual syringes are widely used because they are inexpensive, easily maneuverable, disposable, and do not require complex and bulky driving mechanisms.
Syringes are often used in dispensing high viscosity fluids. For example, in dentistry, high viscosity fluids such as uncured dental filling materials are often dispensed onto small targets such as a pre-drilled tooth cavity. Dispensing high viscosity fluids, however, requires the user to exert a relatively high force on the manual syringe. This required exertion can produce undesired stress and fatigue on the user. Furthermore, dispensing high viscosity fluids can be more difficult to control. For example, because of the high exertion force required to dispense high viscosity materials, it can be difficult to dispense small controlled amounts or to dispense the material at a constant or desired flow rate. The high exertion force can also result in the operator""s hand becoming shaky or unstable. Such shaking and lack of control can result in the fluid missing the target.
In one approach to overcome some of the above problems, devices such as caulking type guns have been used to dispense high viscosity fluids. Caulking type guns have a levered handle which produces a mechanical advantage. Such devices, however, are large and cumbersome relative to conventional syringes. Furthermore, some caulking type guns operate on a ratcheting system which makes it difficult to dispense in a smooth, continuous manner. Finally, since caulking type guns have a handle that orthogonally projects from the barrel, caulking type guns are limited in their use and maneuverability
Therefore, an easily maneuverable apparatus and method are desired for the controlled manual dispensing of high viscosity fluids.
A hydraulic syringe includes a syringe barrel having an exterior surface and an interior surface. A syringe grip outwardly projects from the exterior surface of the syringe barrel. The interior surface of the syringe barrel bounds a chamber having a substantially uniform transverse cross sectional area along its length. Sealed within the chamber is a hydraulic fluid. A manual plunger is coupled with the first end of the barrel so as to selectively advance within the chamber thereof. A hydraulic plunger is slidably disposed within the second end of the barrel. As the manual plunger is advanced, the hydraulic fluid is pressurized which in turn causes the hydraulic plunger to advance.
One of the unique features of the present invention is that the manual plunger has a transverse cross sectional area that is smaller than the maximum transverse cross sectional area of the hydraulic plunger. As a result, a hydraulic advantage is achieved. That is, as the manual plunger is advanced within the chamber under a first force at a first speed, the hydraulic fluid is pressurized. In turn, the pressurized hydraulic fluid pushes against the hydraulic plunger. As a result of the hydraulic plunger having a larger surface area of displacement, the hydraulic plunger moves forward with a second force that is greater than the first force and at a second speed that is slower than the first speed. In turn, this magnified or increased second force is applied through the hydraulic plunger to the high viscosity fluid for dispensing.
Once the material has been dispensed by the hydraulic syringe, a spring disposed between the hydraulic plunger and the second end of the barrel is used to help retract the hydraulic plunger. Furthermore, one or more retraction rods are secured to the hydraulic plunger so as to project towards the first end of the syringe barrel. A guide is mounted on and radially outwardly projects from the manual plunger. Each rod extends through a passageway formed on the guide such that the guide can freely slide along the length of each rod. However, the rods are also formed such that as the manual plunger is retracted, the guide secures to the end of each rod resulting in both the rods and the hydraulic plunger being retracted as the manual plunger is retracted.
In the above embodiment, as a result of the magnification of force, minimal manual force is required to be applied by the user of the hydraulic syringe to effectively dispense high viscosity fluids in a controlled manner. Furthermore, since minimal force and thus minimal exertion is required by the user, fatigue and shaking by the user is also minimized. Finally, since the hydraulic syringe has a configuration similar to a conventional syringe, the hydraulic syringe is convenient and easily maneuvered by the user. That is, rotation of the wrist facilitates quick and easy placement for most delivery angles.
These and other features and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.